The present invention relates to a scroll type compressor, and more particularly to a scroll type compressor which is utilized in refrigeration and air conditioning systems.
A conventional scroll type compressor, which has been disclosed in e.g. Japanese Unexamined Patent Publication No. 80088/1988, is constructed as shown in FIG. 17. In FIG. 17, reference numeral 1 designates a fixed scroll. Reference numeral 2 designates an orbiting scroll. Reference numeral 3 designates a crankshaft. Reference numeral 4 designates a driving bushing which is rotatably mounted in a bearing part 2a formed in the orbiting scroll 2. Reference numeral 5 designates an Oldham's ring. Reference numeral 6 designates a main frame. Reference numeral 6a designates a main bearing which is formed in the main frame 6. Reference numeral 7 designates an electric motor stator. Reference numeral 8 designates an electric motor rotor. Reference numeral 9 designates a sub frame. Reference numeral 9a designates a sub bearing which is formed in the sub frame 9. Reference numeral 10 designates a hermetic shell. Reference numeral 11 designates an intake tube which directs a refrigerant from outside. Reference numeral 12 designates a discharge tube. Reference numeral 13 designates a lubricating oil which is stored in a bottom part of the hermetic shell. The crankshaft 3 has an eccentric shaft portion 3a formed at an upper portion. The eccentric shaft portion 3a is fitted into the bearing part 2a through the driving bushing 4, the bearing part 2a being formed on a base plate undersurface of the orbiting scroll 2. The crankshaft 3 has a main shaft portion 3b and a sub frame shaft portion 3c formed on its upper end and lower end, respectively, so that the main shaft portion 3b is supported by the main bearing 6a of the main frame 6 and the sub shaft part 3c is supported by the sub bearing 9a of the sub frame 9. Reference numerals 14 and 15 designate an upper balance weight and a lower balance weight, respectively, which are attached on the opposite sides (in the vertical direction) of the electric motor rotor 8.
Now, the operation of the conventional scroll type compressor of FIG. 17 will be explained. Torque which is generated by the electric motor is transmitted by the crankshaft 3 which is shrinkage fitted into the rotor 8. The torque is further transmitted to the orbiting scroll 2 through the eccentric shaft portion 3a and the driving bushing 4. The Oldham's ring 5 which works as a rotation preventing mechanism causes the orbiting scroll 2 to carry out such a revolution movement that the orbiting scroll moves along a circular orbit. The revolution movement changes the volume of a compression chamber formed between the fixed scroll 1 and the orbiting scroll 2 to compress the refrigerant.
The refrigerant enters the hermetic shell 10 from an outer refrigeration cycle through the intake tube 11. The refrigerant is compressed in the compression chamber to have a high pressure, and then flows out in the outer refrigeration cycle through the discharge tube 12. By the way, a thrust direction force of compressive loads of the refrigerant which are applied to the orbiting scroll 2 is supported by a thrust bearing surface 6b on an upper end surface of the main frame 6. On the other hand, a radial direction force F.sub.g of the compressive loads is transmitted to the crankshaft 3 through the driving bushing 4 as shown in FIG. 18 . The crankshaft 3 is supported by the main bearing 6a formed in a lower boss of the main frame 6, and by the sub bearing 9a formed in the sub frame 9.
The upper balance weight 14 and the lower balance weight 15 which are mounted on the opposite ends of the rotor 8 are arranged to be balanced against a centrifugal force F.sub.c1 which is generated by the revolution movement of the orbiting scroll 2. Centrifugal forces F.sub.c2 and F.sub.c3 which are generated by the upper balance weight 14 and the lower balance weight 15 are also supported by the main bearing 6a and the sub bearing 9a. The lubricating oil 13 which is stored in the bottom part of the hermetic shell 10 is fed to sliding parts such as the bearing parts and the compression chamber by a centrifugal force caused by the rotation of the crankshaft 3.
In the conventional scroll type compressor, the radial direction force F.sub.9 which is applied to the orbiting scroll in the compression stroke is exerted on the eccentric shaft portion 3a which is at the upper end of the crankshaft 3, as explained. However, because the eccentric shaft portion 3a as the exerting point projects from the main bearing 6a of the main frame 6 in the direction remote from the bearing 9a, the compressive load F.sub.g causes the crankshaft 3 to be flexture-deformed as shown in FIG. 19. When the crankshaft 3 is flexure-deformed, the eccentric shaft portion 3a is inclined in the bearing part 2a of the orbiting scroll 2, the main shaft portion 3b is inclined in the main bearing 6a of the main frame 6, or the sub shaft part 3c is inclined in the sub bearing 9a of the sub frame 9. This creates e.g. a problem in that load carrying capacities of the respective bearing parts can deteriorate to wear or seize the bearing parts.
In particular, recently, the application of a variable speed operation to a compressor under an inverter control is accompanied by extension of the operating range of the compressor from a low speed to a high speed in e.g. air conditioning systems. In a low speed operating area, an oil film is difficult to be formed in the bearings. In a high speed operating area, the centrifugal forces F.sub.c1, F.sub.c2 and F.sub.c3 which are generated by the orbiting scroll 2, the upper balance weight 14 and the lower balance weight 15 are increased to further enlarge the flexture-deformation of the crankshaft 3, making the problem more noticeable, which is demanded to be solved.